A circuit board and a microphone module are described in U.S. Patent Application Publication No. 2012/0177229 A1. A cavity in the form of an acoustic channel, whose connection openings lie in a main surface of the circuit board, is developed in the layer structure of this circuit board. One of the two connection openings is used as sound entry opening, while a microphone component part for the signal acquisition and signal processing is mounted over the other connection opening. Here, the geometry and dimensioning of the acoustic channel are developed in such a way that it forms an acoustic waveguide or resonator for sound waves of a certain frequency range, in particular for voice signals. This is meant to achieve an especially satisfactory sound introduction at the microphone component.
The microphone component parts that are to be used within the framework of the invention discussed here are equipped with at least one MEMS microphone component and possibly also with further MEMS or ASIC components. The packaging technology (AVT) of these components is designed for mounting on a circuit board. For this purpose, the component parts of such a microphone component can be positioned and wired in a shared housing within the framework of the 1st level assembly. However, they may also be combined in one package together with a circuit board carrier or at the wafer level. The microphone sensitivity of such component parts generally depends on the size of the back volume behind the microphone diaphragm of the microphone component. This back volume is usually enclosed during the 1st level assembly of the microphone component, i.e., during its packaging. The type of packaging therefore defines and limits the size of the back volume of the microphone component.